Process for preparing cadmium red pigment



2,111,111 Patented Jan. 15, 19.57

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PROCESS FDR PREPARING CADMIUM RED PIGNENT Benjamin W. Allan and Frank O.Rummery, Baltimore, Md., assignors to The Glidden Company, Cleveland,

'0, a corporation of Ohio No Drawing. Application May 21, 1953, SerialNo. 356,596

20 Claims. (Cl. 106-301) This invention relates to a novel process forpreparing pure or extended cadmium red pigment through the use orange tomaroon. Pure cadmium yellow pigments are composed only of cadmium andsulfur, but When very which is to be coprecipitated with cadmium sulfidewhen preparing raw cadmium red pigment.

In making the pure pigment, the SeO2SeO3 type ever, this is not feasibleWhen barium sulfide solution is used as the sulfidic reactant in makingBHSOQ compositetype pigments. Accordingly, it is another object to pre-'pare crude cadmium red pigment of the pure type by dissolving oxidicselenium compound in the alkali metal sulfide reactant solution.

Further and ancillary objects will be apparent from the followingdescription of the invention.

We have now discovered that a Water-soluble oxidic tated the use ofelemental selenium.

The foremost problem encountered in working out the present inventionwas that of converting the soluble OX"- during the pigment strike totion were used.

In the total reaction, i. e., after addition of the last 20% of thecadmium sulfate solution (29 ml.), it was Neither cadmium nor seleniumWas washed out of the cake.

The Washed precipitate was calcined in a closed tube furnace, thetemperature being raised quickly to 575 C., and then being held for50minutes. The calcined' mass was quenched in distilled Water which hadbeen boiled to remove any dissolved oxygen. The resulting masswas muchdarker in color than the standard maroon and was very. clean and bright.

Example I-n orderi'to produce a color which could be evaluated by meansof the Cadmolith standards, the proportion ofdeoz was reduced by half ascompared with Example- 1.

Seven grams of the same SeOz was added to 130.5 mi. of the cadmiumsulfate solution used in Example 1 and the resulting mixture was treatedwith 200 ml. of sodium sulfide solution, the same as had been used inExample 1. The phi-lwas then 8.5, and in order to prevent the loss ofselenium values 14.5 ml. CdSOt was added, reducing the pH+ to 7.6. Atthis point the selenium was entirely precipitated, but a slight amountof soluble cadmium was present. Upon the addition of a small amount ofsolution containing 1.0 g. NaOH, the soluble cadmium was precipitated,and the selenium remained precipitated, also. Upon washing to removesoluble salts no selenium nor cadmium values were lost.

The washed pigment was calcined as in Example 1, but for only'39 minutesat 575 C., and then was quenched similarly. The resulting pigment had acolor of 85% light red, 15% medium light red and was clean and bright,with a tinting strength over 300% as compared with the cadmium lithoponestandards.

' Exampled In this test the proportion of SeOz was increased 50% overthat of Example 2. The same solutions were used as in Examples 1 and 2.22.82 grams of SeOz was dissolved in 296.4 mi. of cadmium sulfatesolution. The theoretical amount of sodium sulfide (430 ml.) was addedto the mixed selenium-cadmium solution and a pH+ of 8.9 was recorded.15.6 ml. CdSOi was added and the pH+ dropped to 8.1. At this point therewas no appreciable amount of soluble selenium or cadmium.

' The washed pigment was calcined in a closed tube furnace at 600 C. for37 minutes and then was quenched as in Example 1. The pigment had a goodtinting strength and was clean and bright, with a color of 85% mediumred, 15% deep red.

Example 4 The proportion of SeOz over that of Example ,3.

A new sodium sulfide solution was prepared with an OHzSH ratioelf-0.936: 1.00 and a sulfide ion concentration of31.2 g./l.

The mixed solution of 25.0 grams SeOz dissolved in 280.8 ml. of cadmiumsulfate solution had a pH+ of 1.1.

After the sodium sulfide solution had been added, the pH-lof the slurrywas 8.2. Additional cadmium sulfate solution was added, lowering the pH+to approximately 7.0, and the filtrate was free of soluble selenium andcadmium.

The precipitate was filtered and washed, then treated with ammoniumphosphate equivalent to 1% H3PO4, dried and calcined Calcination wasdone in a closed tube furnace at 625 C. for 30 minutes, after which thecalcined mass was quenched. The resulting pigment had a good tintingstrength, was very clean and bright, and had a color corresponding toDeep Red.

was increased 10% Example 5 476 ml. of a barium sulfide solution, at 80contained.33.6 g./l. sulfide ion and a ratio OH:SH=1.019:1.00,

was used as the alkaline-earth sulfide reactant.

sulfate solution, at 'room te ,perature, was adjusted to 1.80 g./1. Cdconcentration- 312ml. of the solution was. treated. with 31.5 gf Oz..ontaining 71.22% Se, whichresulted in a reactant solution with a 11+051.2,.

C., which The two reactant solutions were added simultaneously to thereaction vessel with thorough agitation which insured a completedispersion of the selenium in the resulting precipitate. The final pH+was 7.55. The slurry was diluted with an equal volume of water, filteredand washed. The filter-cake was slurried in a minimum of water andtreated with a small amount of diammonium phosphate conditioning saltand dried at C. The dry cake was crushed and calcined under conditionsexcluding extraneous gases, then quenched in water, filtered and dried.

The product was approximately equal to the cadmium lithopone Deepstandard.

Example 6 430 gallons g./l. Cd, was placed in the strike tank. solutionwas 5.5. 329 pounds of pure SeOz was in'the CdSO4 solution.

The cadmium sulfate solution was agitated rapidly, and barium sulfidesolution containing some dissolved elementary sulfur was added at asteady rate such that the addition was completed in 1 /2 hours. The timeof addition is not entirely critical, but depends on the rate ofagitation, one skilled in the art.

The final pH+ was 8.3. Upon final adjustment with a small quantity ofCdSO4 solution the slurry was agitated for an additional 60 minutes toachieve final equilibrium, then filtered, and washed to remove traces ofsoluble salts.

The washed precipitate was dried and crushed to /2"--1 size preparatoryto calcining. During the calcination air was excluded, but provision wasmade for the escape of gaseous reaction products through a vent stack.The calcination temperature rose to 630 C. in a period of 35 minutes.The batch was then discharged directly into clean water after which itwas ground and treated similarly to any other cadmium red pigment.

Example 7 ml. portion of the same original CdSOi Example 5 was treatedwith selenic acid There resulted a clear waterwhite solution which wasthen reacted with another 476 ml. portion of the original barium sulfidesolution, the same as was used in Example 5. Complete uniformity andhomogeneity of the precipitate was insured by applying adequateagitation in the mixing of the two reactant solutions.

The volume of the resulting raw pigment slurry was doubled by dilutionwith water. The slurry was treated with 1% K2003 on a pigment weightbasis, then filtered, dried, crushed, calcined, and quenched similarlyto the procedure followed in Example 5.

j The product was a light red cadmium lithopone pigment equal in qualityto the Cadmolith standard.

Example 8 Cadmium sulfate solution was used at a concentration of g./ l.Cd and at pH+ 5.5. To 430 gallons was added 193 lbs. of SeOz withagitation to effect the dissolution of theSeOz.

vA BaS solution was employed at 60 C. with a Baum density of 14.5" and aratio OH:SH=1.09: 1.00. A 667 gallon portion of this solution wastreated with 224 lbs. of pure Se and agitated until all of the seleniumwas dissolved in the BaS solution.

The mixed solution of [BaS+Sel was added to, the mixed solution of[CdSOH-SeOzl, gradually, with rapid agitation, over a period of 1 /2hours. Finally, a small portion of 13215 solution was added raising thepH+ to 8.9.. Agitation was continued f r 10. minutes lo ger then theslurry was diluted twofold with water, filtered, dried, crushed, andcalcined in a, rotary furnace. The temperature was raised to 670 C. in32 minutes; the

Another 312 solution used in containing 17.15 g.

dissolved an understanding of which will be clear to any-.

resulting pigment product was quenced in water, filtered and dried.

The final pigment was approximately medium red, of excellent color and ahigh tinting strength.

Example 9 A cadmium sulfate solution was prepared at 180 g./l. Cdconcentration and at 5.5 ph+.

A solution of sodium sulfide was prepared containing 37.2 g./l. sulfideion. The ratio OHzSH was 1.06:1.00. A 200 cc. portion of this NazSsolution was treated with 7 grams 8e02,, and mixed to obtain a uniformsolution of the selenium in the sodium sulfide.

The cadmium sulfate (145 cc.) and the mixed sulfate. soluble cadmiumsalt solutions effectively insolubilizes most of the selenium while alsoprecipitating the cadmium.

It will be understood that good agitation should be maintainedthroughout the strikes, whatever procedure or type of strike is beingused, and that soluble cadmium salts other than cadmium sulfate (e. g.,cadmium nitrate) can be used equally well except where BaSOr-extendedpigments are sought as the direct product of a strike.

narrower ranges than in prior art practices. In other words, whereintervals of 50 C. might be tried in investigating calcining ranges ofprior art practices, one should here employ intervals of only 25 C. oreven less when seeking the optimum range.

Promoters and/or conditioners such as have been used in the past areequally useful here in improving the efiects cf calcination. Theammonium phosphate of Examples 4 and 5 and the potassium carbonate ofExample 7 illusdeterioration of color.

Having described our invention, what we claim is:

1. A process for preparing cadmium red pigment by precipitation andsubsequent calcination which comprises the step of precipitating cadmiumsulfide from aqueous ionic solutions of its component elements andsimultaneously therewith coprecipitating selenium in a waterinsolubleform from an aqueous solution which contains dissolved water-solubleselenium acid radicals selected from the group consisting of seleniousacid radicals, selenic acid radicals and mixtures thereof as a result ofdissolving in said aqueous solution oxidic selenium compound selectedfrom the group consisting of selenium dioxide, selenium trioxide, andmixtures thereof.

2. A process as claimed in claim 1 wherein all of the selenium needed tocombine with said precipitated cadmium sulfide to prepare a calcinedcadmium red pigment of desired shade is provided by said aqueoussolution of dissolved water-soluble selenium acid radicals and issimultaneously coprecipitated therefrom with said cadmium sulfide inaccordance with claim 1.

3. A process as claimed in claim 1 wherein said cadmium sulfide isprecipitated by reacting an aqueous solusolution of cadmium salt.

4. A process as claimed in claim 3 wherein said dissolved oxidicselenium compound provides all of the selenium needed to combine withsaid precipitated cadmium sulfide to form a calcined cadmium red pigmentof desired shade.

5. A process as claimed in claim 4 wherein the dissolved oxidic seleniumcompound is selenium dioxide.

sulfide is precipitated by reacting an aqueous solution of cadmium saltwith an aqueous solution of alkali metal solution of alkali metalsulfide.

8. A process as claimed in claim 7 wherein said dissolved oxidicselenium compound provides all of the selenium needed to combine withsaid precipitated cadmium sulfide to form a calcined cadmium red pigmentof desired shade.

9. A process as claimed in claim 7 wherein the dissolved oxidic seleniumcompound is selenium dioxide.

10. A process as claimed in claim 7 wherein the dissolved oxidicselenium compound is selenium trioxide.

11. A process as claimed in claim 1 wherein said cadsolution of cadmiumsalt.

12. A process as claimed in claim 11 wherein said dissolved oxidicselenium compound provides all of the selenium needed to combine withsaid precipitated cadmium sulfide to form a calcined cadmium red pigmentof desired shade.

13. A process as claimed in claim 12 wherein the dissolved oxidicselenium compound is selenium dioxide.

14. A process as claimed in claim 12 wherein the dissolved oxidicselenium compound is selenium strioxide.

' 15. In a process for preparing pure cadmium red pig- 16. A process asclaimed in claim 15 wherein the oxidic selenium compound which isdissolved is selenium dioxide.

17. A process as claimed in claim 15 wherein the oxidic seleniumcompound which is dissolved is selenium trioxide.

18. In a process for preparing extended cadmium red pigment, saidprocess being of the type wherein cadmium sulfide is precipitated in anaqueous medium by reacting an aqueous solution of cadmium sulfate withan aqueous solution of barium sulfide, wherein selenium in insolubleform is coprecipitated with said cadmium sulfide, and wherein theresulting coprecipitate is calcined to convert it to pigment, theimprovement which comprises dissolving oxidic selenium compound in saidcadmium sulfate solution prior to reacting it with said barium sulfidesolution, said oxidic selenium compound being selected from the groupconsisting of selenium dioxide, selenium trioxide, and miXtures thereof.

19.'A process as claimed in claim 18 wherein said oxidic seleniumcompound provides all of the insoluble selenium which is needed tocombine with said cadmium sulfide to produce a calcined extended cadmiumred pigment of desired shade.

20. A process as V oxidic selenium compound is selenium dioxide.

References Cited in the file of this patent UNITED STATES PATENTSclaimed in claim 19 wherein said 2,134,055 Meister Oct. 25, 19382,360,280 Rolph et al Oct. 10, 1944 2,643,196 Allan et a1. June 23,1953

OTHER REFERENCES Ser. No. 350,065 Lcefler (A. P. 0.), published May 11,1943. a I Journal fiir praktische Chemie, vol. 95, pp.

1. A PROCESS FOR PREPARING CADMIUM RED PIGMENT BY PRECIPITATION ANDSUBSEQUENT CALCINATION WHICH COMPRISES THE STEP OF PRECIPITATING CDMIUMSULFIDE FROM AQUEOUS IONIC SOLUTIONS OF ITS COMPONENT ELEMENTS ANDSIMULTANEOUSLY THEREWITH COPRECIPITATING SELENIUM IN A WATERINSOLUBLEFORM FROM AN AQUEOUS SOLUTION WHICH CONTAINS DISSOLVED WATER-SOLUBLESELENIUM ACID RADICALS SELECTED FROM THE GROUP CONSISTING OF SELENIOUSACID RADICALS, SELENIC ACID RADICALS AND MIXTURES THEREOF AS A RESULT OFDISSOLVING IN SAID AQUEOUS SOLUTION OXIDIC SELENIUM COMPOUND SELECTEDFROM THE GROUP CONSISTING OF SELENIUM DIOXIDE, SELENIUM TRIOXIDE, ANDMIXSTURES THEREOF.